It said it wanted to prevent companies playing off their workforces in different countries against one another.

Amicus is due to merge with the Transport and General Workers Union in May, creating a super-union of two million UK workers.

Derek Simpson, Amicus general secretary, said: “The world is changing and the new global realities involve transnational companies being able to trade-off countries and workforces against each other.

“Our aim is to create a powerful single union that can transcend borders to challenge the global forces of capital and I envisage a functioning, if loosely federal, multinational trade union organisation within the next decade.

“As a single union we will be able to focus on delivering better pay and conditions for our members and have the organising strength to reach out to new trade union members in our existing work places, as well as in new industries.”